Circular array hydrophone simulator

ABSTRACT

A device for simulating time delayed outputs resulting from impingement of a point source of sonic energy upon a nonlinear array of hydrophones. An acoustic signal generator provides an analog output signal to a pulse forming circuit which converts the analog signal to a series pulse train which is fed to a shift register clocked at a rate in accordance with the time delays between the hydrophones. Selected outputs from the register are reconverted to analog signals by individual wave forming circuits assigned to each of the shift register outputs. A plurality of noise generators provide noise signal outputs which are independently added to the reconverted analog signals to form a plurality of selectively delayed signals simulative of hydrophone outputs having both signal and noise components, the delays being variable to simulate different angles of sonic energy approach by selection of appropriate shift register outputs.

ted States tent Kijeslty [4 Nov. 4, 1975 CIRCULAR ARRAY HYDROIPHONEPrimary Examiner-Richard A. Farley SIMULATOR Attorney, Agent, or Firm-R.S. Sciascia; Henry Hansen [75] Inventor: Michael M. Kijesky, Warminster,

Pa. [57] ABS i'i CT 73 Assignee; The United states of America as Adevice for simulating time delayed outputs resulting represented by theSecretary f the from impingement of a point source of sonic energy NavyWashington, DC upon a nonlinear array of hydrophones. An acoustic signalgenerator provides an analog output signal to a [22] Filed: May 2, 1974pulse forming circuit which converts the analog signal to a series pulsetrain which is fed to a shift register [21] Appl' 466n8 clocked at arate in accordance with the time delays between the hydrophones.Selected outputs from the [52] US. Cl. 35/ 10.4 register are reconvertedto analog signals by individual [51] int. Cl. G09B 9/00 wave formingcircuits assigned to each of the shift reg- [58] Field of Search 340/3A, 5 C, 5 R; ister outputs A plurality of noise generators provide 10.4noise signal outputs which are independently added to the reconvertedanalog signals to form a plurality of [56] References Cited selectivelydelayed signals simulative of hydrophone UNITED STATES PATENTS outputshaving both signal and noise components, the 3,363,045 1/1968Pommerening 35/104 deleys being variable to Simulate .different angles.of 3,479,439 11/1969 Kaufman et al. S0910 y pp y Selectlon f PP P3,484,738 12/1969 Autrey 340/ R shlft reglster p 7 Claims, 2 DrawingFigures /Z9 S/G/VAL CL oc/r 67VRA70R Z2 24 PULSE .3 50- 5/7 FORMER 5,475SHIFT REG/$767? 8 -z?/7' NUMBER-*Z 3.5

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US. Patent Nov. 4, 1975 3,916,533

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FIG. 2

CIRCULAR ARRAY HYDROPHONE SIMULATOR BACKGROUND OF THE INVENTION Thepresent invention relates generally to sonar equipment comprising anonlinear array of hydrophones and. in particular. to means forsimulating the time delayed output of each hydrophone within the array.The direction detecting ability of such equipment depends upon the timedelays between impingement of a sonic energy wavefront upon theindividual hydrophones within the array.

The simulated outputs of the nonlinear hydrophone array can be connectedto the input of a beam forming network which operates on the hydrophoneoutputs to provide an indication of the direction from which the sonicenergy point source emmanates. The desirability of a device forsimulating the outputs representative of a nonlinear hydrophone arraybecomes apparent be cause of the obvious problems and limitationsinherent in the use of actual hydrophone arrays in an ocean environment.The application of electronic equipment used for simulatingprogressively delayed outputs representative of a linear hydrophonearray is well known in the art and particularly pointed out in US. Pat.No. 3.484.738 to Autrey. issued Dec. 16, 1969. The prior art. however.does not teach structure to resolve the more complex situation ofsimulating the outputs from a nonlinear hydrophone array.

SUMMARY OF THE INVENTION Accordingly, it is an object of the presentinvention to provide apparatus for achieving predetermined time delaysof a generated, acoustic signal so as to provide a plurality ofsimulated nonlinear array hydrophone outputs which outputs can beapplied to a beam forming network for use in the testing of sonarequipment.

Another object of the present invention is to provide a nonlinear arrayhydrophone output device which will simulate the arrival of a sonicenergy wave front for any predetermined direction utilizing a minimum ofequipment and space.

Yet another object of the present invention is to more truly simulatethe delayed outputs from the nonlinear array by the addition ofrespective noise signals to each of the selected hydrophone outputs.

Still another object of the present invention is to accomplish thesimulation of outputs resulting from the impingement of sonic energy ona nonlinear array of hydrophones from preselected directions through theprovision of a multiple tap shift register means for providing outputsat preselected delay times indicative of the positions of each of thehydrophones within the nonlinear array relative to the energy pointsource. the simulated direction of approach of the sonic energy beingchangeable by changing the output taps of the shift register.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an example of a nonlineararray having four equally spaced hydrophones configured in a circle forsimulation by the present invention; and

FIG. 2 is a block diagram of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, thereis shown a circular hydrophone array 10, which is one example of annonlin- 2 car array configuration, having four hydrophones 12a-l2dspaced equally about the circumference of the array 10. For purposes ofexplanation and by way of example the array 10 is placed within acoordinate system having a vertical axis Y and a horizontal axis X whichintersect at the center of the array. Accordingly, the array 10 lies inthe X-Y plane and. when viewed in three-dimensional space, has a polaraxis Z (not shown) normal to the X-Y plane and which goes through thecenter of the array 10. For simplicity in the embodiment of FIG. 1, asonic energy point source S has been placed within the plane of thearray 10 and external to the circle. Of course. the source S can beplaced at any position with respect to the nonlinear array to simulatediffering approach directions for an acoustic wave front. Accordingly.an angle 6 (not shown). which is the angle formed between the polar axisZ and the point source S in this example, is For purposes ofcalculations to be described later and further identification ofelements within the array 10, the hydrophones 12a-l2d will be consideredaccording to the alphabetical order of the postscripts. The position ofthe energy source S is identified in this example as being at an angle 090 and at an angle q5,, 60, the angle (1),, being measured from a firstline drawn be tween the center of the array 10 and the first consideredhydrophone 12a and a second line drawn from the center of the circle tothe point source S. Accordingly, it may be seen from the geometry of theexample shown in FIG. 1 that the acoustic wave front generated by thepoint source S will impinge upon the array 10 by first coming in contactwith hydrophone 121; and then hydrophones 12a, 12c, and 12d in order.The particular time at which each hydrophone will be impinged upon bythe wavefront generated by the source S is illustrated by drawingindividual lines beginning at each hydrophone position whichorthogonally intersect with the bearing of the point source S relativeto the center of the array 10. Accordingly. the intersection of theacoustic wave front with an initial impingement upon hydrophone 12boccurs at time I. Hydrophones 120. 12c and 12d are sequentially impingedupon by the acoustic wave front at times t and 1 respectively.

Referring now to FIG. 2 there is shown a block diagram of the presentinvention. An acoustic signal generator 20 provides an output which isconnected to the input of a pulse former 22 whose output is applied tothe input of a fifty bit shift register 26 through a gate 24. A clock 28provides simultaneous outputs to the enable input of the gate 24 and tothe clock input of the register 26. The shift register 26 provides 50outputs of which only four are shown (bit numbers 1, 8, 28, 35) and theparticular selection of which will later be explained. Corresponding tothe output bit numbers I, 8, 28, and 35 are shift register output lines30a, 30b. 30c". and 3011, respectively. Each of the output lines30(1-3011 is respectively connected to inputs of wave formers 32a32z1.the outputs of which are respectively con nected to one input ofrespective summing circuits 36a-36d. Noise generators 34(1-3411 arerespectively connected to second inputs of the summing circuits 36a36dwhose respective individual outputs are shown at terminals 38a-38d.

Referring to FIG. 1, the initial calculations for the operation of theinvention will now be explained. The initial conditions for the circulararray output simulator are created by preselecting the number ofhydrophone elements within the nonlinear array and. in the circulardrophones 12Zzl2d which, for purposes of simple illustration define aplane that includes the energy source S. The polar axis Z providesabasis for polar coordination of the array. Accordingly, the source Slies at a polar angle of 6" 90 from the polar axis Z, if viewed'inthree-dimensional space. Hydrophon'e 12a is arbitrarily chosen to be thefirst element within the array and is conveniently placed on thevertical axis Y. The energy source S, being within the plane of thearray, is chosen in this example to. be positioned at an azimuthal angle(1),, 60 as measured from a radius extending to the first hydrophone12a. Obviously, the number of hydrophone elements within the array, theradius, and the relative position of the energy source S may all be individually selected so as to encompass a wide variety of sonar conditionssuitable for simulation. The energy source S, for example, need only bedefined as having a polar angle 6 relative to the polar axis Z and theazimuthal angled) relative to the arbitrarily chosen first hydrophoneelement within the array. Also illustrated in FIG. 1 is a series ofsonic energy wave fronts which are generated by the energy source S' anddirected towards the center of the circular array 10. The energysource'S'generates sonic energy within the acoustic frequency rangeand,in this example, has arbitrarily been chosen to be 100 Hertz.

Given the foregoing initial conditions, the linear phase displacementP,, of each hydrophone within the circular array 10 relative to theposition of the energy source S can be calculated according to theequation:

, p,,.= R SIN 0 Cos (dm- 4%.)

wherein: R theradius of the circle in feet, 0 the polar angle; and theangle measured from the first hydrophone element to nth hydrophoneelement with the array.

Since' both the angles 0 and d) are considered in the phase relationshipfor the circular array, a beam former used in conjunction with theinvention 'is capable of forming a beam which is selective in both theazimuthal and polar directions. Utilizing the foregoing formula, thephase displacement of the first hydrophone 12a relative to the energysource S is easily calculated to be 0.5 feet. This distance isrepresentative of the difference between a line drawn from the firsthydrophone 120 normal to the direction of the energy source S (and shownin' FIG. 1 as that line delineating t and the center of the circulararray. Assuming that the velocity of sound in water is approximately5000 feet per second, the time required T for the energy source wavefront to travel from the first hydrophone 12a to the center of the arrayis easily calculated to be 0.1 millisecond (ms.). Similarly, therequired times T T T for the wave front to travel, respectively, betweenhydro phones 12b,12c', 12d and the center of the circular I array arecalculated to be 0.17 ms., 0.1 ms. and 0.17 msfThe wave front timedelays between progressively impinged hydrophones within the array maynow be calculated by noting the time differences between the tion isadopted that hy d rophone 12b is first impinged upon at I 0',hydrophonel2a will be impinged upon by the wave front at 2 0.07milliseconds later. The next hydrophone 120 to be activated by the wavefront is impinged relative to the hydrophone 12b at 1 T T 0.27milliseconds. Similarly, the output of hydrophone 12d is activatedrelative to hydrophone 12b at T T 0.34 milliseconds. Therefore, the timenecessary for .the wave front to traverse the first and last impingedelementswithin the array i.e., hydrophones 12 b and 12d, respectively,is 0.34 ms.

Other nonlinear hydrophone arrays configurations such as, for example,volumetric designs may also be simulated in light of the foregoingteachings by appropriate mathematical implementation corresponding tothe geometry 'of the array to be simulated withrespect to the positionof a sonic energy point source. That is, the differing arrival'times ofa sonic energy wave front with respect to individual hydrophones withinthe nonlinear array may be' ascertained by calculating the respectivephase displacement distances between each of hydrophones relative to thepoint source position.

Referring now to FIG. 2, the signal generator 20 generates an acousticsignal of approximately hertz which is connected'to a conventional pulseformer 22 which, for example, may comprise clipping circuitry whichconverts the incoming analog acoustic signal to a series pulse trainhaving a digital format. The clock 28 provides a series of highfrequency pulses having a frequency, for example, of 100 Kilohertzsimultaneously to the enable input of a gate 24 and a clock input of ashift register 26. The frequency of the clock 28 and the number of bitswithin the register 26 are predetermined so that when interacting withone another the shift register 26 is clocked at a rate consistent withthe desired resolution of the simulated delay times between thehydrophone outputs, and the number of bits within the register issufficient to handle the maximum delay time between'the first and lastactivated hydrophones within the'array. Accordingly, within the presentembodiment having a maximum delay time of 0.34 milliseconds. anappropriate delay time resolution element would be 0.01 milliseconds perregister bit. The choice of a maximum delay'time resolution element,and, correspondingly, the minimum clocking frequency, is most easilydetermined by noting the greatest common denominator for the delay'times between the progressively impinged hydrophones. in the presentexample, the se-- quential delay times are t 0, t 0.07 ms., t 0.27 ms.and r 0.34 ms. Therefore,'by selecting a delay time resolution elementof 0.01 ms. per register bit, it is assured that all of the hydrophoneoutputs can be accurately simulated in time andbe represented by aparticular register bit'output. In order that each bit within theregister 26 be progressively shifted every 0.01 milliseconds, the clock28 will therefore have a frequency of 100 Kilohertz. The number of bitsrequired in the shift register to adequately represent a total delaytime of 0.34 milliseconds with a shifting rate of 0.01 milliseconds perbit is 35. A conventional 50 bit serial shift register 26 was choseninasmuch as this bit capacity is readily available. Of course,greaterbit capacities and clocking frequencies may be used in order to increasethe resolution of the time delay elements if so desired. Once theclocking frequency is determined, the minimum number of bits required inthe shift register may be calculated by adding one bit to the product ofthe clock frequency and the time required for the wave front to traversebetween the first and last impinged hydrophones. In the present example.the minimum number of bits required N,,,,-,, l (100 X (0.34 X 10 35.Alternatively, the minimum number of bits may be calculated by addingone bit to the quotient of the time between the first and last impingedhydrophones and the maximum delay time resolution element. The gate 24is therefore enabled by the clock 28 at a 100 Kilohertz rate and passesthe pulse train from the pulse former 22 to the serial input of the 50bit shift register 26. The shift register 26 provides 50 parallel bitoutputs of which only four are shown. Particular outputs of the register26 are selectively chosen to simulate time delays between the varioushydrophones within the array 10. For example, bit number 1 output havingan output line 30a corresponds to the time activation of hydrophone 12a.Similarly. output bit numbers 8, 28, and having output lines 3012, 30c,30:! represent sonar activity from hydrophones 12b, 12c. and 120'.respectively. A conventional wave former 321) comprising. for example. alow pass filter, is connected to receive an output signal from the firstbit position within the shift register 26 corresponding to the firsthydrophone 12b to be activated by the energy source S. Similarly, 0.07milliseconds or 7 bit positions later, an output signal from bit number8 of the register 26 is connected to the input of wave former 32acorresponding to the next activated hydrophone 12a within the array. Awave former 320 is connected to receive an output signal 0.27milliseconds or 27 bit positions later than the output signal producedat bit output position number 1. Accordingly, the register 26 isselectively tapped at output bit number 28 to provide a digitized outputcorresponding to the next succeedingly acti' vated hydrophone 12c".Lastly. 0.34 milliseconds or 34 bit positions from bit number 1 output,the register 26 is selectively tapped at bit number 35 output to form aninput to wave former 32d corresponding to the last activated hydrophone12:]. Each of the wave formers 32a32d operates to reconstitute thedigital output from the shift register into an analog representation ofthe original acoustic signal. Of course, the individual outputs of thewave formers are now selectively delayed in time to represent theprogressive activation of the hydrophones 120-1211 by the energy sourceS. Conventional summing circuits 36a-36z1 such, as, for example. linearfrequency mixers are connected to receive the reconstituted analogsignals from respective wave formers 32a32d. Noise generators 34a-34dgenerate random noise simulative of noise found within an oceanenvironment and provide individual noise output signals which areconnected respectively to inputs of the summing circuits 3611-3611. Eachof the summers 36u36d independently mixes the reconstituted acous' ticsignal from the output of the wave formers 32a-32d with the noisegenerated by the generators 34(1-3411 and provides outputs having bothsignals and noise components simulative of an ocean environment at respective output terminals 38(1-3841.

Thus it may be seen that it has been provided a novel device forsimulating delayed outputs from a circular array of hydrophones for anywave front direction.

Obviously many modifications and variations of the invention arepossible in light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

1. Apparatus for simulating the progressively delayed outputs resultingfrom impingement of sonic energy having a point source on a nonlineararray of hydrophones, comprising:

signal generating means for providing an analog output signal having afrequency simulative of the point source; pulse forming means connectedto receive said analog output signal for converting the analog outputsignal into a digital pulse train output signal;

clock means for providing clock pulses at predetermined equal intervals;

delay means connected to receive said clock pulses and said digitalpulse train output signal for providing a plurality of outputs eachrepresentative of the pulse train but serially delayed by one interval;and

a plurality of wave forming means corresponding to the number ofhydrophones in the nonlinear array respectively connected to receivepreselected ones of said delay means outputs for converting said delaymeans outputs to analog output signals. said preselected ones of delaymeans outputs corresponding to the predicted impingement times of thesonic energy at the respective hydrophones; plurality of noisegenerating means for producing random noise output signals simulative ofa water body; and

a plurality of summing means having a first input connected to receiverespective ones of said noise generating means outputs signals and asecond input connected to receive respective ones of said wave formingmeans analog output signals for respectively summing the noise andanalog signals to form output signals simulative of individualhydrophone outputs within said nonlinear array.

2. Apparatus according to claim 1 wherein the maxi mum value ofrespective ones of the equal pulse intervals is equal to the greatestcommon denominator relative to the time delays betwen said hydrophoneoutputs.

3. Apparatus according to claim 2 wherein the minimum number of saiddelay means outputs is equal to one plus the quotient of the timedifference between the first and last impinged. hydrophones within thenonlinear array, and the maximum pulse interval.

4. Apparatus according to claim 3 wherein said delay means furthercomprises:

gating means connected to receive said digital pulse train and saidclock pulses for gating said pulse train upon the occurrence ofrespective ones of said clock pulses and for providing an outputthereof; and

multiple tap shift register means connected to receive said gating meansoutput and said clock pulses for repetitively shifting said gating meansoutput according to said clock pulses and for providing said delay meansoutputs.

5. Apparatus according to claim 4 wherein said pulse forming meanscomprises a clipping circuit.

6. Apparatus according to claim 5 wherein each of said \vave formingmeans comprises a low pass filter.

7. Apparatus according to claim 6 wherein each of said summing meanscomprises a linear frequency mixer.

1. Apparatus for simulating the progressively delayed outputs resultingfrom impingement of sonic energy having a point source on a nonlineararray of hydrophones, comprising: signal generating means for providingan analog output signal having a frequency simulative of the pointsource; pulse forming means connected to receive said analog outputsignal for converting the analog output signal into a digital pulsetrain output signal; clock means for providing clock pulses atpredetermined equal intervals; delay means connected to receive saidclock pulses and said digital pulse train output signal for providing aplurality of outputs each representative of the pulse train but seriallydelayed by one interval; and a plurality of wave forming meanscorresponding to the number of hydrophones in the nonlinear arrayrespectively connected to receive preselected ones of said delay meansoutputs for converting said delay means outputs to analog outputsignals, said preselected ones of delay means outputs corresponding tothe predicted impingement times of the sonic energy at the respectivehydrophones; a plurality of noise generating means for producing randomnoise output signals simulative of a water body; and a plurality ofsumming means having a first input connected to receive respective onesof said noise generating means outputs signals and a second inputconnected to receive respective ones of said wave forming means analogoutput signals for respectively summing the noise and analog signals toform output signals simulative of individual hydrophone outputs withinsaid nonlinear array.
 2. Apparatus according to claim 1 wherein themaximum value of respective ones of the equal pulse intervals is equalto the greatest common denominator relative to the time delays betwensaid hydrophone outputs.
 3. Apparatus according to claim 2 wherein theminimum number of said delay means outputs is equal to one plus thequotient of the time difference between the first and last impingedhydrophones within the nonlinear array, and the maximum pulse interval.4. Apparatus according to claim 3 wherein said delay means furthercomprises: gating means connected to receive said digital pulse trainand said clock pulses for gating said pulse train upon the occurrence ofrespective ones of said clock pulses and for providing an outputthereof; and multiple tap shift register means connected to receive saidgating means output and said clock pulses for repetitively shifting saidgating means output according to said clock pulses and for providingsaid delay means outputs.
 5. Apparatus according to claim 4 wherein saidpulse forming means comprises a clipping circuit.
 6. Apparatus accordingto claim 5 wherein each of said wave forming means comprises a low passfilter.
 7. Apparatus according to claim 6 wherein each of said summingmeans comprises a linear frequency mixer.